[DCCP]: Fix skb->cb conflicts with IP

dev_queue_xmit() and the other IP output functions expect to get a skb
with clear or properly initialized skb->cb. Unlike TCP and UDP, the
dccp_skb_cb doesn't contain a struct inet_skb_parm at the beginning,
so the DCCP-specific data is interpreted by the IP output functions.
This can cause false negatives for the conditional POST_ROUTING hook
invocation, making the packet bypass the hook.

Add a inet_skb_parm/inet6_skb_parm union to the beginning of
dccp_skb_cb to avoid clashes. Also add a BUILD_BUG_ON to make
sure it fits in the cb.

[ Combined with patch from Gerrit Renker to remove two now unnecessary
  memsets of IPCB(skb)->opt ]

Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 0 insertions, 1 deletions

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 474075adbde4..b33704415555 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -489,7 +489,6 @@ static int dccp_v4_send_response(struct sock *sk, struct request_sock *req,
 
                 dh->dccph_checksum = dccp_v4_csum_finish(skb, ireq->loc_addr,
                                                               ireq->rmt_addr);
-                memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
                 err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
                                             ireq->rmt_addr,
                                             ireq->opt);